Single-step metal bond and contact formation for solar cells

ABSTRACT

A method for fabricating a solar cell is disclosed. The method can include forming a dielectric region on a surface of a solar cell structure and forming a first metal layer on the dielectric region. The method can also include forming a second metal layer on the first metal layer and locally heating a particular region of the second metal layer, where heating includes forming a metal bond between the first and second metal layer and forming a contact between the first metal layer and the solar cell structure. The method can include forming an adhesive layer on the first metal layer and forming a second metal layer on the adhesive layer, where the adhesive layer mechanically couples the second metal layer to the first metal layer and allows for an electrical connection between the second metal layer to the first metal layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/436,282, filed on Feb. 17, 2017, which is a continuation of U.S.patent application Ser. No. 14/874,254, filed on Oct. 2, 2015, now U.S.Pat. No. 9,577,139, issued on Feb. 21, 2017, which is a continuation ofU.S. patent application Ser. No. 14/137,918, filed on Dec. 20, 2013, nowU.S. Pat. No. 9,178,104, issued on Nov. 3, 2015, the entire contents ofwhich are hereby incorporated by reference herein.

TECHNICAL FIELD

Embodiments of the subject matter described herein relate generally tosolar cells. More particularly, embodiments of the subject matter relateto solar cell fabrication processes and structures.

BACKGROUND

Solar cells are well known devices for converting solar radiation toelectrical energy. A solar cell has a front side that faces the sunduring normal operation to collect solar radiation and a backsideopposite the front side. Solar radiation impinging on the solar cellcreates electrical charges that may be harnessed to power an externalelectrical circuit, such as a load. The external electrical circuit mayreceive electrical current from the solar cell by way of metal fingersthat are connected to doped regions of the solar cell.

BRIEF SUMMARY

In an embodiment, a method for fabricating a solar cell is disclosed.The method can include forming a dielectric region on a surface of asolar cell structure. The method can also include forming a first metallayer on the dielectric region. The method can include forming a secondmetal layer on the first metal layer and locally heating a particularregion of the second metal layer, where heating includes forming a metalbond between the first and second metal layer and forming a contactregion between the first metal layer and the solar cell structure.

In an embodiment, a method for fabricating a solar cell is disclosed.The method can include forming a dielectric region on a surface of asolar cell structure. The method can also include forming a first metallayer on the dielectric region. The method can include forming anadhesive layer on the first metal layer and forming a second metal layeron the adhesive layer, where the adhesive layer mechanically couples thesecond metal layer to the first metal layer and allows for an electricalconnection between the second metal layer to the first metal layer.

In an embodiment, a solar cell fabricated using any of the above methodsis disclosed.

These and other features of the present disclosure will be readilyapparent to persons of ordinary skill in the art upon reading theentirety of this disclosure, which includes the accompanying drawingsand claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the subject matter may be derived byreferring to the detailed description and claims when considered inconjunction with the following figures, wherein like reference numbersrefer to similar elements throughout the figures.

FIG. 1 is a flow chart representation of an example method forfabricating of a solar cell, according to some embodiments;

FIG. 2 is a cross-section of a first and second metal layer on a solarcell structure;

FIG. 3 is a cross-section of locally heating a second metal layer,according to some embodiments;

FIG. 4 is a cross-section of forming a metal bond, according to someembodiments;

FIG. 5 is a cross-section of forming a contact, according to someembodiments;

FIG. 6 is a cross-section of an example solar cell fabricated accordingto the disclosed techniques;

FIG. 7 is a schematic plan view of example for a metal layers, accordingto some embodiments;

FIG. 8 is a flow chart representation of another example method forfabricating of a solar cell, according to some embodiments;

FIG. 9 is a cross-section of an adhesive layer formed on a first metallayer, according to some embodiments;

FIG. 10 is a cross-section of a second metal layer formed on an adhesivelayer, according to some embodiments;

FIG. 11 is a cross-section of another example solar cell fabricatedaccording to the disclosed techniques;

FIG. 12 is a cross-section of still another example solar cellfabricated according to the disclosed techniques;

FIG. 13 is a flow chart representation of still another an examplemethod for fabricating of a solar cell, according to some embodiments;

FIG. 14 is a cross-section of an adhesive layer formed on a first metallayer, according to some embodiments;

FIG. 15 is a cross-section of a second metal layer formed on an adhesivelayer, according to some embodiments;

FIG. 16 is a cross-section of metal bonds, contacts and a cured adhesivelayer, according to some embodiments;

FIG. 17 is a cross-section of forming a patterned metal layer, accordingto some embodiments;

FIG. 18 is a cross-section of an example solar cell fabricated accordingto the disclosed techniques; and

FIG. 19 is a cross-section of still another example solar cellfabricated according to the disclosed techniques.

DETAILED DESCRIPTION

The following detailed description is merely illustrative in nature andis not intended to limit the embodiments of the subject matter or theapplication and uses of such embodiments. As used herein, the word“exemplary” means “serving as an example, instance, or illustration.”Any implementation described herein as exemplary is not necessarily tobe construed as preferred or advantageous over other implementations.Furthermore, there is no intention to be bound by any expressed orimplied theory presented in the preceding technical field, background,brief summary or the following detailed description.

This specification includes references to “one embodiment” or “anembodiment.” The appearances of the phrases “in one embodiment” or “inan embodiment” do not necessarily refer to the same embodiment.Particular features, structures, or characteristics may be combined inany suitable manner consistent with this disclosure.

Terminology. The following paragraphs provide definitions and/or contextfor terms found in this disclosure (including the appended claims):

“Comprising.” This term is open-ended. As used in the appended claims,this term does not foreclose additional structure or steps.

“Configured To.” Various units or components may be described or claimedas “configured to” perform a task or tasks. In such contexts,“configured to” is used to connote structure by indicating that theunits/components include structure that performs those task or tasksduring operation. As such, the unit/component can be said to beconfigured to perform the task even when the specified unit/component isnot currently operational (e.g., is not on/active). Reciting that aunit/circuit/component is “configured to” perform one or more tasks isexpressly intended not to invoke 35 U.S.C. § 112, sixth paragraph, forthat unit/component.

“First,” “Second,” etc. As used herein, these terms are used as labelsfor nouns that they precede, and do not imply any type of ordering(e.g., spatial, temporal, logical, etc.). For example, reference to a“first” solar cell does not necessarily imply that this solar cell isthe first solar cell in a sequence; instead the term “first” is used todifferentiate this solar cell from another solar cell (e.g., a “second”solar cell).

“Coupled”—The following description refers to elements or nodes orfeatures being “coupled” together. As used herein, unless expresslystated otherwise, “coupled” means that one element/node/feature isdirectly or indirectly joined to (or directly or indirectly communicateswith) another element/node/feature, and not necessarily mechanically.

In addition, certain terminology may also be used in the followingdescription for the purpose of reference only, and thus are not intendedto be limiting. For example, terms such as “upper”, “lower”, “above”,and “below” refer to directions in the drawings to which reference ismade. Terms such as “front”, “back”, “rear”, “side”, “outboard”, and“inboard” describe the orientation and/or location of portions of thecomponent within a consistent but arbitrary frame of reference which ismade clear by reference to the text and the associated drawingsdescribing the component under discussion. Such terminology may includethe words specifically mentioned above, derivatives thereof, and wordsof similar import.

Although much of the disclosure is described in terms of solar cells forease of understanding, the disclosed techniques and structures applyequally to other semiconductor structures (e.g., silicon wafersgenerally).

The formation of metal regions, such as positive and negative busbarsand contact fingers to doped regions on a solar cell can be achallenging process. Techniques and structures disclosed herein improveprecision throughput and cost for related fabrication processes.

In the present disclosure, numerous specific details are provided, suchas examples of structures and methods, to provide a thoroughunderstanding of embodiments. Persons of ordinary skill in the art willrecognize, however, that the embodiments can be practiced without one ormore of the specific details. In other instances, well-known details arenot shown or described to avoid obscuring aspects of the embodiments.

FIG. 1 illustrates a flow chart of an embodiment for an examplefabrication method for a solar cell. In various embodiments, the methodof FIG. 1 can include additional (or fewer) blocks than illustrated. Forexample, in one embodiment, partially removing the dielectric region ona particular region, block 104, may not be performed. The method of FIG.1 can also be performed on a solar cell structure with N-type and P-typedoped regions. Note that the method of FIG. 1 can be performed at thecell level during fabrication of the solar cell or at the module levelwhen the solar cell is connected and packaged with other solar cells.

As shown in 102, a dielectric region, which can also be referred to as adielectric layer, can be formed on a surface of a solar cell structure.In an embodiment, the dielectric region can be formed over an N-typedoped region and a P-type doped region of the solar cell structure. Inone embodiment, the dielectric region is a continuous and conformallayer that is formed by blanket deposition. In an embodiment, thedielectric region can be formed by screen printing, spin coating, or bydeposition and patterning, for example, such that the dielectric regionis not continuous. In an embodiment, the dielectric region can includesilicon nitride, silicon oxide, silicon oxynitride, aluminum oxide,amorphous silicon or polysilicon.

At 104, the dielectric region can be partially removed to expose/form acontact region. In an embodiment, the contact region can allow for theformation of a contact, such as an ohmic contact. In an embodiment, thedielectric region is partially removed on a particular region, where theparticular region is aligned over a N-type doped region or a P-typedoped region of the solar cell structure. As mentioned above, note thatin some embodiments, block 104 may not be performed and, as a result,the dielectric region may not be partially removed.

At 106, a first metal layer can be formed on the dielectric region. Inone embodiment, the first metal layer is a continuous and conformallayer that is formed by blanket deposition. In another embodiment, thefirst metal layer is non-continuous (e.g., printed in a particularpattern or deposited and then etched into the particular pattern). In anembodiment, forming a metal layer can include performing a physicalvapor deposition, screen printing, sintering, plating, or laser transferprocess. In an embodiment, the first metal layer can also be referred toas a seed metal layer. In an embodiment, forming the first metal layercan include depositing a seed metal layer on the dielectric region. Inan embodiment, the first metal layer can include a metal such as, butnot limited to, copper, tin, aluminum, silver, gold, chromium, iron,nickel, zinc, ruthenium, palladium, or platinum and their alloys. In anembodiment, the first metal layer can be a patterned metal layer, suchas a first patterned metal layer. In an embodiment, the first patternedmetal layer can be placed, deposited or aligned on the dielectricregion.

As shown in 108, a second metal layer can be formed on the first metallayer. In one embodiment, the second metal layer is a continuous andconformal layer that is formed by blanket deposition. In an embodiment,the second metal layer can include a metal foil. In an embodiment, thesecond metal layer can include metal such as, but not limited to,copper, tin, aluminum, silver, gold, chromium, iron, nickel, zinc,ruthenium, palladium, or platinum and their alloys. In an embodiment,the second metal layer can be a patterned metal layer, such as a secondpatterned metal layer (e.g., a patterned metal foil). In an embodiment,the second patterned metal layer can be placed, deposited or aligned onthe dielectric region.

At 110, a metal bond and a contact can be formed in a single process. Inan embodiment, forming a metal bond and a contact in a single processincludes locally heating a particular region of the second metal layer.In an embodiment, locally heating on a particular region of the secondmetal layer allows for heat transfer from the second metal layer to aparticular region in-between the first and second metal layer andsubsequently, the heat further transfers through the first metal layerto a particular region between the first metal layer and the dielectricregion forming a contact. In an embodiment, the formed metal bond canelectrically and mechanically couple the second metal layer to the firstmetal layer. In an embodiment, the contact can electrically andmechanically couple the first metal layer to the solar cell structure.

In one embodiment, locally heating includes directing a laser beam onthe second metal layer. In an embodiment, directing the laser beam onthe second metal layer can weld the second metal layer to the firstmetal layer. In an embodiment, the laser beam can have a pulse durationin the range of 1 nanosecond to 10 milliseconds. In an embodiment, thelaser beam can be generated using a continuous wave (CW) laser or apulsed laser. In an embodiment, the laser beam has a wavelength in therange of 100 nanometers—12 microns. In an embodiment, the laser beam canbe directed on a metal foil, to form a metal bond with a seed metallayer and further form an ohmic contact between the seed metal layer andthe solar cell structure. In an embodiment, the metal bond and ohmiccontact are aligned with a particular region of the solar cellstructure. In an embodiment, the particular region of the solar cell canbe aligned to a P-type doped region or an N-type doped region. In anembodiment, the second metal layer or metal foil can be a patternedmetal foil (e.g., in a finger pattern, such as an interdigitated fingerpattern). In an embodiment, the patterned metal foil can be placed onthe seed metal layer. Note that, in some embodiments, non-laser basedwelding techniques can be used to form the metal bond and contact in asingle process. In an embodiment, portions of the first and second metallayer can be removed in an interdigitated pattern prior to locallyheating.

The embodiments above can be performed for multiple solar cells. Forexample, in one embodiment, a metal foil (e.g., corresponding to and/orincluding contact fingers for multiple cells) can be aligned and placedon a first solar cell and a second solar cell. The metal foil can thenbe coupled to both a first and second solar cell according to the methodof FIG. 1.

FIGS. 2-7 are cross-sectional views that schematically illustrate amethod of fabricating a solar cell in accordance with an embodiment ofthe present disclosure.

With reference to FIG. 2, a solar cell during a fabrication process isshown that includes a second metal layer 232 placed on a first metallayer 230, where the first metal layer 230 is placed on a solar cellstructure 200. In an embodiment, the first metal layer 230 can have athickness in the range of 1-5 microns, for example the first metal layer230 can be in the range of approximately 1-2 microns. In an embodiment,the second metal layer 232 can have a thickness in the range of 1-100microns (e.g. a metal foil), for example the second metal layer 232 canbe approximately 50 microns. As shown, the solar cell structure 200 caninclude a silicon substrate 208, a first doped region 210 or a seconddoped region 212 and a dielectric region 220. The solar cell of FIG. 2can also include a front side 204, configured to face the sun duringnormal operation of the solar cell and a back side 202 opposite thefront side 204. As discussed above, the first metal layer or secondmetal layer 230, 232 can include a metal such as, but not limited to,copper, tin, aluminum, silver, gold, chromium, iron, nickel, zinc,ruthenium, palladium, or platinum and their alloys. In an embodiment,the dielectric region 220 can include silicon nitride, silicon oxide,silicon oxynitride, aluminum oxide, amorphous silicon or polysilicon Inan embodiment, the first doped region 210 or the second doped region 212can include a P-type doped region or an N-type doped region of thesilicon substrate 208.

FIG. 3 illustrates locally heating the second metal layer 232. In anembodiment, locally heating on a particular region of the second metallayer 232 can be performed using a laser beam 262 from a laser source260. In an embodiment, locally heating can be performed on a particularregion of the second metal layer 232 using an electron beam.Subsequently, heat 264 from the laser beam 262 is transferred to thesecond metal layer 232. In an embodiment, the laser beam 262 can bedirected to the second metal layer 232 using a galvanometer, scanningstage or using conventional optical interfacing and control equipment,systems and processes.

With reference to FIG. 4, the formation of a metal bond 242 is shown. Inan embodiment, heat 264 from the laser beam 262 is transferred throughthe second metal layer 232 to a region between the first and secondmetal layer 230, 232 forming a metal bond 242, where the metal bond 242allows for an electrical connection between the first and second metallayer 230, 232. In an embodiment, the second metal layer can bepartially removed or melted due to the heat 264 as shown in FIG. 4. Inan embodiment, the metal bond 242 can mechanically couple the secondmetal layer 232 to the first metal layer 230.

FIG. 5 illustrates the formation of a contact 240. In an embodiment,heat 264 from the laser beam 262 is further transferred through thefirst metal layer 230 to a region between the first metal layer 230 andthe doped regions 210, 212, where the heat 264 forms a contact 240,allowing for an electrical connection between the first metal layer 230and the doped regions 210, 212. As described above, the contact 240 canbe an ohmic contact. In an embodiment, the dielectric region 220 may notbe dissociated during the above process, allowing for an electricalconnection between the first metal layer 230 and the doped regions 210,212 with the dielectric region 220 between the first metal layer 230 andthe doped regions 210, 212 essentially intact (e.g. continuous). In anembodiment, the contact 240 can mechanically couple the first metallayer 230 to the solar cell structure 200.

In an embodiment, the steps shown in FIGS. 3, 4 and 5 can all beperformed in single process. In a single process can include changingcharacteristics of the tool (e.g., laser) used to perform the process.For example, the initial laser pulse can be a higher power pulse toperform one of the bonds followed by a change to a lower power pulse toform the other bond. Laser characteristic/configuration changes otherthan power can include pulse duration, shape of the pulse, wavelength,etc. In performing the steps of FIGS. 3-5 in a single process, multiplefabrication steps can be removed, i.e. to from a metal bond and an ohmiccontact separately, thereby improving solar cell fabrication efficiencyand reducing cost.

With reference to FIG. 6, a solar cell subsequent to the single-stepprocess performed in FIGS. 3-5 is shown. The solar cell of FIG. 6 caninclude a front side 204, configured to face the sun during normaloperation of the solar cell and a back side 202 opposite the front side.As shown, the solar cell can include a solar cell structure 200. Thesolar cell 200 structure can include a silicon substrate 208, first andsecond doped regions 210, 212 and a dielectric region 220. In anembodiment, the dielectric regions 220 can be formed in-between contacts240. The solar cell structure 200 is coupled to the first metal layer230 by a contact 240, such as an ohmic contact. In an embodiment, thecontact 240 can mechanically couple the first metal layer 230 to thesolar cell structure 200. The first metal layer 230 is coupled to thesecond metal layer 232 by a metal bond 242. In an embodiment, the metalbond 242 can mechanically couple the second metal layer 232 to the firstmetal layer 230. Contact fingers, made up of the first and second metallayers 230, 232 are separated at separation 234. It is to be noted thatan electrical connection at the separation 234 could allow for anelectrical short and can be detrimental to the performance of the solarcell. The gap or separation 234 can be formed by a laser ablationprocess or an etching process, removing excess metal from the first andsecond metal layers 230, 232. In an embodiment, the first and seconddoped regions can be P-type and N-type doped regions, respectively. Inan embodiment, the dielectric region 220 can be patterned such that someareas do not have dielectric regions under the first metal layer 230. Inan embodiment, the first metal layer 230 can have a thickness in therange of 1-5 microns, for example the first metal layer 230 can be inthe range of approximately 1-2 microns. In an embodiment, the secondmetal layer 232 can have a thickness in the range of 1-100 microns (e.g.a metal foil), for example the second metal layer 232 can beapproximately 50 microns.

FIG. 7 illustrates example metal layers 250, 252. In an embodiment, themetal layers 230, 232 (from FIGS. 2-6 above) can be formed in a metalstrip 250 as shown. In an embodiment, multiple metal strips 250 can beused to from an interdigitated pattern. In an embodiment, theinterdigitated pattern can include positive contact fingers, negativecontact fingers, positive busbar and a negative busbar. In anembodiment, the metal layers 230, 232 can be formed in round or dottedpattern 252. There is no limitation to the patterns the metal layers230, 232 can form and FIG. 7 merely illustrates some possible patternswhich can be used. The front and back side 204, 202 of the solar cell isshown for reference.

With reference to FIG. 8, a flow chart of an embodiment for anotherexample fabrication method for a solar cell is shown. In variousembodiments, the method of FIG. 8 can include additional (or fewer)blocks than illustrated. The method of FIG. 8 can also be performed on asolar cell structure with N-type and P-type doped regions. Similar tothe above, the method of FIG. 8 can be performed at the cell levelduring fabrication of the solar cell or at the module level when thesolar cell is connected and packaged with other solar cells.

As shown in 302, a dielectric region, which can also be referred to as adielectric layer, can be formed on a surface of a solar cell structure.In an embodiment, the dielectric region can be formed over an N-typedoped region and a P-type doped region of the solar cell structure. Inone embodiment, the dielectric region is a continuous and conformallayer that is formed by blanket deposition. The dielectric region can beformed by screen printing, spin coating, or by deposition andpatterning, for example, such that the dielectric region is notcontinuous. In an embodiment, the dielectric region can include siliconnitride, silicon oxide, silicon oxynitride, aluminum oxide, amorphoussilicon or polysilicon. In an embodiment, the dielectric region can bepartially removed to expose/form a contact region. In an embodiment, thecontact region can allow for the formation of a contact, such as anohmic contact. In an embodiment, the dielectric region is partiallyremoved on a particular region, where the particular region is alignedover a N-type doped region or a P-type doped region of the solar cellstructure. As mentioned above, note that in some embodiments, thedielectric region may not be partially removed.

At 304, a first metal layer can be formed on the dielectric region. Inone embodiment, the first metal layer is a continuous and conformallayer that is formed by blanket deposition. In another embodiment, thefirst metal layer is non-continuous (e.g., printed in a particularpattern or deposited and then etched into the particular pattern). In anembodiment, forming a metal layer can include performing a physicalvapor deposition, screen printing, sintering, plating, or laser transferprocess. In an embodiment, the first metal layer can also be referred toas a seed metal layer. In an embodiment, the first metal layer caninclude a metal foil. In an embodiment, forming the first metal layercan include depositing a seed metal layer on the dielectric region. Inan embodiment, the first metal layer can include a metal such as, butnot limited to, copper, tin, aluminum, silver, gold, chromium, iron,nickel, zinc, ruthenium, palladium, or platinum and their alloys. In anembodiment, the first metal layer can include a patterned metal layer,such as a first patterned metal layer. In an embodiment, the firstpatterned metal layer can be placed, deposited or aligned on thedielectric region.

At 306, an adhesive layer can be formed on the first metal layer, and insome embodiments, also on the dielectric region (e.g., filling in gapsbetween a patterned first metal layer). In an embodiment, the adhesivelayer can be formed by screen printing, ink-jet printing, spin coating,casting, lamination or by deposition and patterning, for example. In anembodiment, the adhesive layer can be formed by a Chemical VaporDeposition (CVD) or a Physical Vapor Deposition (PVD) method. In anembodiment, the adhesive layer can be an insulating adhesive layer. Inan embodiment, the adhesive layer can be a uniform low viscosityadhesive layer. In an embodiment, the adhesive layer can be patterned,whether patterned as it is formed, or formed and then patterned (e.g.,etched). In an embodiment, forming an adhesive layer can include forminga conductive adhesive layer. In an embodiment, forming an adhesive layercan include forming an anisotropically conductive adhesive layer.

As shown in 308, a second metal layer can be formed on the adhesivelayer. In one embodiment, the second metal layer is a continuous andconformal layer that is formed by blanket deposition. In an embodiment,the adhesive layer can provide structural support, mechanically couplingthe second metal layer to the first metal layer, and can also allow thesecond metal layer to be in electrical connection with the first metallayer. In an embodiment, the second metal layer can include a metalfoil. In an embodiment, the second metal layer can include metal suchas, but not limited to, copper, tin, aluminum, silver, gold, chromium,iron, nickel, zinc, ruthenium, palladium, or platinum and their alloys.In an embodiment, the second metal layer can include a patterned metallayer, such as a second patterned metal layer (e.g., a patterned metalfoil). Note that in an embodiment, forming the first metal layer caninclude any of the blocks described above. Using a patterned adhesivelayer can allow for the formation of the second metal layer using adirect physical vapor deposition (PVD) process. In an embodiment, theadhesive layer can be cured subsequent to the formation of the secondmetal layer. In an embodiment, forming the second metal layer caninclude forming a metal foil on the adhesive layer. In an embodiment,direct contact between the first and second metal layers can beperformed by applying pressure to the second metal layer (e.g., byvacuum, a roller, a squeegee, etc.).

Similar to the above, a metal bond and a contact can be formed. In anembodiment, the metal bond and contact can be formed separately or in asingle-step process as discussed above.

The embodiments above can be performed for multiple solar cells. Forexample, in one embodiment, a metal foil (e.g., including contactfingers for multiple cells) can be aligned and placed on a first solarcell and a second solar cell. The metal foil can then be coupled to botha first and second solar cell. Also, the above can be performed to forvarious types of solar cells, such as front contact and back contactsolar cells.

FIGS. 9-12 are cross-sectional views that schematically illustrate amethod of fabricating a solar cell in accordance with an embodiment ofthe present disclosure. Unless otherwise specified below, the numericalindicators used to refer to components in FIGS. 9-12 are similar tothose used to refer to components or features in FIGS. 2-7 above, exceptthat the index has been incremented by 200.

FIG. 9 illustrates a solar cell during a fabrication process mentionedabove. The solar cell of FIG. 9 includes an adhesive layer 470 formed ona first metal layer 430, where the first metal layer 430 is placed on asolar cell structure 400. In an embodiment, the adhesive layer 470 canbe formed by screen printing, ink-jet printing, spin coating, casting,lamination or by deposition (CVD or PVD) and patterning. As shown, thesolar cell structure 400 can include a silicon substrate 408, a firstdoped region 410 or a second doped region 412 and a dielectric region420. In an embodiment, the first metal layer 430 can also be referred toas a seed metal layer. In an embodiment, forming the first metal layer430 can include depositing a seed metal layer on the dielectric region420. In an embodiment, the first metal layer 430 can include a metalsuch as, but not limited to, copper, tin, aluminum, silver, gold,chromium, iron, nickel, zinc, ruthenium, palladium, or platinum andtheir alloys. In an embodiment, the first metal layer 430 can include apatterned metal layer, such as a first patterned metal layer (e.g., apatterned metal foil). In an embodiment, forming the first metal layer430 can include placing a patterned metal layer on the dielectric region420 separated by a gap 474, where the gap 474 can separate positive andnegative contact fingers. In an embodiment, a laser ablation process canbe performed to form a patterned metal layer. In an embodiment, the gap474 can be formed through laser ablation or etching. In an embodiment,the dielectric region 420 can include silicon nitride, silicon oxide,silicon oxynitride, aluminum oxide, amorphous silicon or polysilicon. Inan embodiment, the first doped region 410 or the second doped region 412can include a P-type doped region or an N-type doped region of thesilicon substrate 408. As mentioned above, the adhesive layer 470 can bean insulating adhesive layer. In an embodiment, the adhesive layer 470can be a uniform low viscosity adhesive layer. In an embodiment, theadhesive layer 470 can be a patterned adhesive layer. In an embodiment,forming an adhesive layer 470 can include forming an anisotropicallyconductive adhesive layer.

FIG. 10 illustrates a second metal layer 432 placed on the adhesivelayer 470. In an embodiment, the adhesive layer 470 can providestructural support, mechanically coupling the second metal layer 432 tothe first metal layer 430. In an embodiment, the second metal layer 432can include a metal foil. In an embodiment, the second metal layer 432can include metal such as, but not limited to, copper, tin, aluminum,silver, gold, chromium, iron, nickel, zinc, ruthenium, palladium, orplatinum and their alloys. In an embodiment, the second metal layer 432can include a patterned metal layer, such as a second patterned metallayer. In an embodiment, forming the second metal layer 432 can includeplacing a patterned metal layer on the adhesive layer 470. In anembodiment, the adhesive layer 470 can be cured subsequent to theformation of the second metal layer 432. In an embodiment, forming thesecond metal layer 432 can include forming a metal foil on the adhesivelayer 470. Provided with a patterned adhesive layer, such as shown at470 in FIG. 10, an embodiment can include curing the patterned adhesivelayer prior to forming a second metal layer 432. In an embodiment,forming a patterned adhesive layer can allow for the formation of thesecond metal layer 432 using a direct physical vapor deposition (PVD)process. In an embodiment, a patterned adhesive layer can be formed suchthat openings can be allowed within the patterned adhesive layer for thesecond metal layer 432 to contact the first metal layer 430, furtherallowing embodimets, similar to the PVD process discussed, to form thesecond metal layer 432 on the first metal layer 430. Also a patternedadhesive layer can allow for the second metal layer 432 to be inelectrical connection with the first metal layer 430. In an embodiment,the adhesive layer 470 can be cured to form a cured adhesive layer. Inan embodiment, forming the second metal layer 432 can include forming ametal foil on the adhesive layer 470. In an embodiment, direct contactbetween the first and second metal layers 430, 432 can be performed byapplying pressure to the second metal layer 432.

With reference to FIG. 11, a solar cell subsequent to the processperformed in FIGS. 9 and 10 is shown. The solar cell of FIG. 11 caninclude a front side 404, configured to face the sun during normaloperation of the solar cell and a back side 402 opposite the front side.As shown, the solar cell of FIG. 11 includes a solar cell structure 400.The solar cell 400 structure can include a silicon substrate 408, firstand second doped regions 410, 412 and a dielectric region 420. The solarcell structure 400 is coupled to the first metal layer 430 by a contact440, such as an ohmic contact. In an embodiment, the contact 440 canmechanically couple the first metal layer 430 to the solar cellstructure 400. The first metal layer 430 is coupled to the second metallayer 432 by a metal bond 442. In an embodiment, the metal bond 442 canmechanically couple the second metal layer 432 to the first metal layer430. Contact fingers, made up of the first and second metal layers 430,432 are separated 474. Any electrical connection at the separation 474can allow for an electrical short and be detrimental to the performanceof the solar cell. The gap or separation 474 can be formed through anetching process or via a laser ablation process where excess metal canbe removed from the first and second metal layers 430, 432. In anembodiment, the first and second doped regions 410, 412 can be P-typeand N-type doped regions. The solar cell of FIG. 11 includes a metalbond 442 and a contact 440. In an embodiment, the metal bond 442 and thecontact 440 can be formed using a laser weld process, either separatelyor in a single-step process as described above. In an embodiment, thecontact 440 can be an ohmic contact. In an embodiment, the metal bond442 and the contact 440 can be formed using any of the methods describedabove. In an embodiment, the dielectric region 420 can be patterned suchthat some areas do not have dielectric regions under the first metallayer 430. In an embodiment, the first metal layer 430 can have athickness in the range of 1-5 microns, for example the first metal layer430 can be in the range of approximately 1-2 microns. In an embodiment,the second metal layer 432 can have a thickness in the range of 1-100microns (e.g. a metal foil), for example the second metal layer 432 canbe approximately 50 microns.

FIG. 12 illustrates another solar cell subsequent to the processperformed in FIGS. 9 and 10. The solar cell of FIG. 12 can include afront side 404, configured to face the sun during normal operation ofthe solar cell and a back side 402 opposite the front side. As shown,the solar cell can include a solar cell structure 400. The solar cell400 structure can include a silicon substrate 408, first and seconddoped regions 410, 412 and a dielectric region 420. In one embodiment,the first metal layer 431 is composed of a plurality of metal particles.In an embodiment, the plurality of metal particles includes aluminumparticles. In an embodiment, the solar cell structure 400 can be coupledto the first metal layer 431 by a contact 440, such as an ohmic contact.In an embodiment, the contact 440 can mechanically couple the firstmetal layer 431 to the solar cell structure 400. In one embodiment, thefirst metal layer 431 is in electrical connection with the second metallayer 432, where the adhesive layer, such as a cured adhesive layer 472,allows for the electrical connection without a metal bond or weld. In anembodiment, the adhesive layer 472 can mechanically couple the secondmetal layer 432 to the first metal layer 430. Contact fingers, made upof the first and second metal layers 430, 432 are separated 474. Anyelectrical connection at the separation 474 can allow for an electricalshort and be detrimental to the performance of the solar cell. The gapor separation 474 can be formed by a laser ablation process or byetching, removing excess metal from the first and second metal layers430, 432. In an embodiment, the first and second doped regions 410, 412can be P-type and N-type doped regions, respectively. In an embodiment,the dielectric region 420 can be patterned such that some areas do nothave dielectric regions under the first metal layer 430. In anembodiment, the first metal layer 431 can have a thickness in the rangeof 1-5 microns, for example the first metal layer 431 can be in therange of approximately 1-2 microns. In an embodiment, the second metallayer 432 can have a thickness in the range of 1-100 microns (e.g. ametal foil), for example the second metal layer 432 can be approximately50 microns.

Note that while the example of FIGS. 9-12 illustrate the first metallayer being patterned before forming the second metal layer on top ofthe adhesive layer and first metal layer, in other embodiments, thesecond metal layer can be formed on top of the adhesive layer and firstmetal layer. In various embodiments, patterning can take place afterforming the first metal layer, after forming the first metal layer andadhesive layer, after forming all three layers, or at multiple stages inthe process (e.g., after forming the first metal layer, and then alsoafter forming the adhesive and second metal layers).

With reference to FIG. 13, a flow chart of an embodiment for stillanother example fabrication method for a solar cell is shown. In variousembodiments, the method of FIG. 13 can include additional (or fewer)blocks than illustrated. For example, in one embodiment, partiallyremoving the dielectric region, block 504, need not be performed. Themethod of FIG. 13 can also be performed on a solar cell structure withN-type and P-type doped regions. Similar to the above, the method ofFIG. 13 can be performed at the cell level during fabrication of thesolar cell or at the module level when the solar cell is connected andpackaged with other solar cells.

As shown in 502, a dielectric region, which can also be referred to as adielectric layer, can be formed on a surface of a solar cell structure.In an embodiment, the dielectric region can be formed over an N-typedoped region and a P-type doped region of the solar cell structure. Inone embodiment, the dielectric region is a continuous and conformallayer that is formed by blanket deposition. The dielectric region can beformed by any of the methods described above such as screen printing,spin coating, or by deposition and patterning for example, such that thedielectric region is not continuous. In an embodiment, the dielectricregion can include silicon nitride, silicon oxide, silicon oxynitride,aluminum oxide, amorphous silicon or polysilicon. In an embodiment, thedielectric region can be partially removed from the dielectric regionforming a contact region. In an embodiment, the contact region can allowfor the formation of a contact, such as an ohmic contact.

At 504, the dielectric region can be partially removed to expose/from acontact region. In an embodiment, the contact region can allow for theformation of a contact, such as an ohmic contact. In an embodiment, thedielectric region is partially removed on a particular region, where theparticular region is aligned over a N-type doped region or a P-typedoped region of the solar cell structure. As mentioned above, note thatin some embodiments, block 504 may not be performed and, as a result,the dielectric region may not be partially removed.

At 506, a first metal layer can be formed on the dielectric region. Inan embodiment, the first metal layer is a first patterned metal layer,and the first patterned metal layer can be placed on the dielectricregion. Note that, in one embodiment, the metal layer can be patternedafter it is applied/formed whereas in other embodiments, the metal layercan be applied in a particular pattern. In one embodiment, the firstmetal layer is a continuous and conformal layer that is formed byblanket deposition. In an embodiment, forming a metal layer can includeperforming a physical vapor deposition, screen printing, sintering,plating, or laser transfer process. In an embodiment, the first metallayer can also be referred to as a seed metal layer. In an embodiment,forming the first metal layer can include depositing a seed metal layeron the dielectric region. In an embodiment, the first metal layer caninclude a metal such as, but not limited to, copper, tin, aluminum,silver, gold, chromium, iron, nickel, zinc, ruthenium, palladium, orplatinum and their alloys. In an embodiment, a laser ablation process oretching can be performed to form the first patterned metal layer.

At 508, an adhesive layer can be formed on the first metal layer and onthe dielectric region. In an embodiment, the adhesive layer can be aninsulating adhesive layer. In an embodiment, the adhesive layer can beformed by screen printing, ink-jet printing, spin coating, casting,lamination or by deposition and patterning, for example. In anembodiment, the adhesive layer can be formed by a Chemical VaporDeposition (CVD) or a Physical Vapor Deposition (PVD) method. In anembodiment, the adhesive layer can be a uniform low viscosity adhesivelayer. In an embodiment, the adhesive layer can be a patterned adhesivelayer. In an embodiment, forming an adhesive layer can include forming aconductive adhesive layer. In an embodiment, forming an adhesive layercan include forming an anisotropically conductive adhesive layer. In anembodiment, the adhesive layer can provide additional structuralsupport, such as mechanically coupling the second metal layer to thefirst metal layer.

As shown in 510, a second metal layer can be formed on the adhesivelayer. In an embodiment, the adhesive layer can provide structuralsupport, mechanically coupling the second metal layer to the first metallayer. In one embodiment, the second metal layer is a continuous andconformal layer that is formed by blanket deposition. In an embodiment,the second metal layer can include a metal foil. In an embodiment, thesecond metal layer can include metal such as, but not limited to,copper, tin, aluminum, silver, gold, chromium, iron, nickel, zinc,ruthenium, palladium, or platinum and their alloys. In an embodiment,the adhesive layer can be cured subsequent to the formation of thesecond metal layer. In an embodiment, forming the second metal layer caninclude forming a metal foil on the adhesive layer.

At 512, a metal bond and a contact can be formed by locally heating aparticular region on the second metal layer. In an embodiment, locallyheating a particular region of the second metal layer allows for heattransfer from the second metal layer to a particular region in-betweenthe first and second metal layer forming the metal bond. Subsequently,the heat can further transfer through the first metal layer to aparticular region between the first metal layer and the dielectricregion forming a contact. In an embodiment, locally heating includesdirecting a laser beam on the second metal layer. In an embodiment, anyof the methods described above can be used to from the metal bond andcontact, either separately or in a single-step process. In anembodiment, the formed metal bond can electrically and mechanicallycouple the second metal layer to the first metal layer. In anembodiment, the contact can electrically and mechanically couple thefirst metal layer to the solar cell structure.

At 514, metal from the second metal layer can be partially removed toform a second patterned metal layer. In an embodiment, the adhesivelayer, or insulating adhesive layer, protects the solar cell structurefrom damage during the said partially removing process. In anembodiment, a laser ablation process can be used to remove excess metalfrom the second metal layer. In an embodiment, the adhesive layerabsorbs excess laser radiation from the laser beam, protecting thedielectric region and solar cell structure from damage. In anembodiment, the adhesive layer can be a heat insulation layer, fromlaser damage, and an electrical insulation layer, between the first andsecond metal layers. In an embodiment, an etching process can be used toremove excess metal.

The embodiments above can be performed for multiple solar cells. Forexample, in one embodiment, a metal foil (e.g., including contactfingers for multiple cells) can be aligned and placed on a first solarcell and a second solar cell. The metal foil can then be coupled to botha first and second solar cell. Also, the above can be performed to forvarious types of solar cells, such as front contact and back contactsolar cells.

FIGS. 14-19 are cross-sectional views that schematically illustrate amethod of fabricating a solar cell in accordance with an embodiment ofthe present disclosure. Unless otherwise specified below, the numericalindicators used to refer to components in FIGS. 14-19 are similar tothose used to refer to components or features in FIGS. 9-12 above,except that the index has been incremented by 200.

FIG. 14 illustrates a solar cell during a fabrication process mentionedabove. The solar cell of FIG. 14 includes an adhesive layer 670 formedon a first metal layer 630 and the dielectric region 620, where thefirst metal layer 630 is placed on a solar cell structure 600. In anembodiment, the adhesive layer 670 can be formed by screen printing,ink-jet printing, spin coating, casting, lamination or by deposition(CVD or PVD) and patterning. As shown, the solar cell structure 600 caninclude a silicon substrate 608, a first doped region 610 or a seconddoped region 612 and a dielectric region 620. In an embodiment, thefirst metal layer 630 can also be referred to as a seed metal layer. Inan embodiment, forming the first metal layer 630 can include depositinga seed metal layer on the dielectric region 620. In an embodiment, thefirst metal layer 630 can include a metal such as, but not limited to,copper, tin, aluminum, silver, gold, chromium, iron, nickel, zinc,ruthenium, palladium, or platinum and their alloys. In an embodiment,the first metal layer 630 can include a patterned metal layer, such as afirst patterned metal layer. In an embodiment, forming the first metallayer 630 can include placing a patterned metal layer on the dielectricregion 620. In an embodiment, a laser ablation process can be performedto form a patterned metal layer. In an embodiment, the dielectric region620 can include silicon nitride, silicon oxide, silicon oxynitride,aluminum oxide, amorphous silicon or polysilicon. In an embodiment, thefirst doped region 610 or the second doped region 612 can include aP-type doped region or an N-type doped region of the silicon substrate608. As mentioned above, the adhesive layer 670 can be an insulatingadhesive layer. In an embodiment, the adhesive layer 670 can be auniform low viscosity adhesive layer. In an embodiment, forming anadhesive layer 670 can include forming an anisotropically conductiveadhesive layer.

With reference to FIG. 15, a second metal layer 632 placed on theadhesive layer 670 is shown. In an embodiment, the adhesive layer 670can provide structural support, mechanically coupling the second metallayer 632 to the first metal layer 630. In an embodiment, the secondmetal layer 632 can include a metal foil. In an embodiment, the secondmetal layer 632 can include metal such as, but not limited to, copper,tin, aluminum, silver, gold, chromium, iron, nickel, zinc, ruthenium,palladium, or platinum and their alloys. In an embodiment, the adhesivelayer 670 can be cured 680 subsequent to the formation of the secondmetal layer 632. In an embodiment, curing can include heating theadhesive layer 670. In an embodiment, the curing can form a curedadhesive layer 672 as shown in FIG. 16. In an embodiment, forming thesecond metal layer 632 can include forming a metal foil on the adhesivelayer 670. In an embodiment, direct contact between the first and secondmetal layers 630, 632 can be performed by applying pressure to thesecond metal layer 632.

FIG. 16 illustrates a cured adhesive layer 672, a metal bond 642 and acontact 640. In an embodiment, the metal bond 642 and a contact 640 canbe formed separately or in a single-step process as discussed above.

With reference to FIG. 17, metal from the second metal layer 632 can bepartially removed to form a second patterned metal layer. In anembodiment, the adhesive layer, cured adhesive layer 672, or insulatingadhesive layer, protects the solar cell structure 600 from damage duringthe said process of partially removing the second metal layer 632. In anembodiment, a laser ablation process can be used to remove excess metalfrom the second metal layer 632. In an embodiment, the adhesive layer orcured adhesive layer 672 absorbs excess laser radiation from a laserbeam 662 from a laser source 660, protecting the dielectric region 620and solar cell structure 600 from damage. In an embodiment, the adhesivelayer can be a heat insulation layer, from i.e. laser damage as shown,and an electrical insulation layer.

FIG. 18 illustrates a solar cell subsequent to the process performed inFIGS. 14-17. The solar cell of FIG. 18 can include a front side 604,configured to face the sun during normal operation of the solar cell anda back side 602 opposite the front side. As shown, the solar cell ofFIG. 18 includes a solar cell structure 600. The solar cell 600structure can include a silicon substrate 608, first and second dopedregions 610, 612 and a dielectric region 620. The solar cell structure600 is coupled to the first metal layer 630 by a contact 640, such as anohmic contact. In an embodiment, the contact 640 can mechanically couplethe first metal layer 630 to the solar cell structure 600. The firstmetal layer 630 is coupled to the second metal layer 632 by a metal bond642. In an embodiment, the metal bond 642 can mechanically couple thesecond metal layer 632 to the first metal layer 630. Contact fingers,made up of the first and second metal layers 630, 632 are separated. Theadhesive layer, such as a cured adhesive layer 672, can be betweencontact fingers and electrically insulating contact fingers of oppositepolarity. In an embodiment, the first and second doped regions 610, 612can be P-type and N-type doped regions. The solar cell of FIG. 18includes a metal bond 642 and a contact 640. In an embodiment the metalbond 642 and the contact 440 can be formed using a laser weld process,either separately or in a single-step process as described above. In anembodiment, the contact 640 can be an ohmic contact. In an embodiment,the dielectric region 620 can be patterned such that some areas do nothave dielectric regions under the first metal layer 630. In anembodiment, the first metal layer 630 can have a thickness in the rangeof 1-5 microns, for example the first metal layer 630 can be in therange of approximately 1-2 microns. In an embodiment, the second metallayer 632 can have a thickness in the range of 1-100 microns (e.g. ametal foil), for example the second metal layer 632 can be approximately50 microns.

With reference to FIG. 19, another solar cell subsequent to the processperformed in FIGS. 14-17 is shown. The solar cell of FIG. 19 can includea front side 604, configured to face the sun during normal operation ofthe solar cell and a back side 602 opposite the front side. As shown,the solar cell can include a solar cell structure 600. The solar cell600 structure can include a silicon substrate 608, first and seconddoped regions 610, 612 and a dielectric region 620. In one embodiment,the first metal layer 631 is composed of a plurality of metal particles.In an embodiment, the plurality of metal particles can include aluminumparticles. In an embodiment, the solar cell structure 600 can be coupledto the first metal layer 631 by a contact 640, such as an ohmic contact.In an embodiment, the contact 640 can mechanically couple the firstmetal layer 630 to the solar cell structure 600. In one embodiment, thefirst metal layer 631 is in electrical connection with the second metallayer 632, where the adhesive layer, such as a cured adhesive layer 672,allows for the electrical connection without a metal bond or weld. In anembodiment, the adhesive layer can mechanically couple the second metallayer 632 to the first metal layer 630. Contact fingers, made up of thefirst and second metal layers 630, 632 are separated. The adhesivelayer, such as a cured adhesive layer 672, can be electrically insulatecontact fingers of opposite polarity. In an embodiment, the first andsecond doped regions 610, 612 can be P-type and N-type doped regions. Inan embodiment, the dielectric region 620 can be patterned such that someareas do not have dielectric regions under the first metal layer 631. Inan embodiment, the first metal layer 631 can have a thickness in therange of 1-5 microns, for example the first metal layer 631 can be inthe range of approximately 1-2 microns. In an embodiment, the secondmetal layer 632 can have a thickness in the range of 1-100 microns (e.g.a metal foil), for example the second metal layer 632 can beapproximately 50 microns.

The embodiments above can be performed for multiple solar cells (e.g.,including contact fingers for multiple cells). Also, the above can beperformed to for various types of solar cells, such as front contact andback contact solar cells.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or embodiments described herein are not intended tolimit the scope, applicability, or configuration of the claimed subjectmatter in any way. Rather, the foregoing detailed description willprovide those skilled in the art with a convenient road map forimplementing the described embodiment or embodiments. It should beunderstood that various changes can be made in the function andarrangement of elements without departing from the scope defined by theclaims, which includes known equivalents and foreseeable equivalents atthe time of filing this patent application.

What is claimed is:
 1. A solar cell, comprising: a polysilicon region ona surface of a solar cell structure; a first metal layer on thepolysilicon region; a second metal layer on the first metal layer; alocalized metal bond between a portion of the first metal layer and aportion of the second metal layer, wherein the first metal layer iselectrically connected to the solar cell structure at a locationdirectly beneath and in alignment with the localized metal bond, whereinthe first metal layer, the second metal layer and the localized metalbond form a conductive contact for the location of the solar cell, andwherein the conductive contact is separated from a neighboring secondconductive contact by a gap that extends to the polysilicon region. 2.The solar cell of claim 1, wherein the first metal layer is electricallyconnected to the solar cell structure beneath the localized metal bondthrough an opening in the polysilicon region.
 3. The solar cell of claim1, wherein the first metal layer is electrically connected to the solarcell structure by an Ohmic contact between the first metal layer and thesolar cell structure.
 4. The solar cell of claim 1, wherein the secondmetal layer is a metal foil.
 5. The solar cell of claim 4, wherein themetal foil comprises a metal selected from the group consisting ofcopper, tin, aluminum, silver, gold, chromium, iron, nickel, zinc,ruthenium, palladium, and platinum.
 6. The solar cell of claim 1,wherein the first metal layer is a metal seed layer.
 7. The solar cellof claim 6, wherein the metal seed layer comprises a metal selected fromthe group consisting of copper, tin, aluminum, silver, gold, chromium,iron, nickel, zinc, ruthenium, palladium, and platinum.
 8. The solarcell of claim 1, wherein the first metal layer and the second metallayer have a same interdigitated pattern.
 9. The solar cell of claim 1,wherein the solar cell structure is an N-type doped region.
 10. Thesolar cell of claim 1, wherein the solar cell structure is a P-typedoped region.
 11. A solar cell, comprising: an amorphous silicon regionon a surface of a solar cell structure; a first metal layer on theamorphous silicon region; a second metal layer on the first metal layer;a localized metal bond between a portion of the first metal layer and aportion of the second metal layer, wherein the first metal layer iselectrically connected to the solar cell structure at a locationdirectly beneath and in alignment with the localized metal bond, whereinthe first metal layer, the second metal layer and the localized metalbond form a conductive contact for the location of the solar cell, andwherein the conductive contact is separated from a neighboring secondconductive contact by a gap that extends to the amorphous siliconregion.
 12. The solar cell of claim 11, wherein the first metal layer iselectrically connected to the solar cell structure beneath the localizedmetal bond through an opening in the amorphous silicon region.
 13. Thesolar cell of claim 11, wherein the first metal layer is electricallyconnected to the solar cell structure by an Ohmic contact between thefirst metal layer and the solar cell structure.
 14. The solar cell ofclaim 11, wherein the second metal layer is a metal foil.
 15. The solarcell of claim 14, wherein the metal foil comprises a metal selected fromthe group consisting of copper, tin, aluminum, silver, gold, chromium,iron, nickel, zinc, ruthenium, palladium, and platinum.
 16. The solarcell of claim 11, wherein the first metal layer is a metal seed layer.17. The solar cell of claim 16, wherein the metal seed layer comprises ametal selected from the group consisting of copper, tin, aluminum,silver, gold, chromium, iron, nickel, zinc, ruthenium, palladium, andplatinum.
 18. The solar cell of claim 11, wherein the first metal layerand the second metal layer have a same interdigitated pattern.
 19. Thesolar cell of claim 11, wherein the solar cell structure is an N-typedoped region.
 20. The solar cell of claim 11, wherein the solar cellstructure is a P-type doped region.